U.S. patent application number 12/288864 was filed with the patent office on 2009-07-02 for thermionic electron emission device and method for making the same.
This patent application is currently assigned to Tsinghua University. Invention is credited to Shou-Shan Fan, Kai-Li Jiang, Liang Liu, Peng Liu.
Application Number | 20090167137 12/288864 |
Document ID | / |
Family ID | 40797316 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090167137 |
Kind Code |
A1 |
Liu; Peng ; et al. |
July 2, 2009 |
Thermionic electron emission device and method for making the
same
Abstract
A thermionic electron emission device includes an insulating
substrate, and one or more grids located thereon. The one or more
grids include(s) a first, second, third and fourth electrode
down-leads located on the periphery thereof, and a thermionic
electron emission unit therein. The first and second electrode
down-leads are parallel to each other. The third and fourth
electrode down-leads are parallel to each other. The first and
second electrode down-leads are insulated from the third and fourth
electrode down-leads. The thermionic electron emission unit
includes a first electrode, a second electrode, and a thermionic
electron emitter. The first electrode and the second electrode are
separately located and electrically connected to the first
electrode down-lead and the third electrode down-lead respectively.
Wherein the thermionic electron emitter includes a carbon nanotube
film structure.
Inventors: |
Liu; Peng; (Beijing, CN)
; Liu; Liang; (Beijing, CN) ; Jiang; Kai-Li;
(Beijing, CN) ; Fan; Shou-Shan; (Beijing,
CN) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. Steven Reiss
458 E. LAMBERT ROAD
FULLERTON
CA
92835
US
|
Assignee: |
Tsinghua University
Beijing City
CN
HON HAI Precision Industry CO., LTD.
Tu-Cheng City
TW
|
Family ID: |
40797316 |
Appl. No.: |
12/288864 |
Filed: |
October 23, 2008 |
Current U.S.
Class: |
313/306 ;
445/22 |
Current CPC
Class: |
H01J 2201/196 20130101;
H01J 1/14 20130101; H01J 31/127 20130101; H01J 9/04 20130101 |
Class at
Publication: |
313/306 ;
445/22 |
International
Class: |
H01J 1/46 20060101
H01J001/46; H01J 9/00 20060101 H01J009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 2007 |
CN |
200710125672.5 |
Claims
1. A thermionic electron emission device comprising: an insulating
substrate; one or more grids located on the insulating substrate,
wherein the one or more grids comprises: a first, second, third and
fourth electrode down-leads located on the periphery of the gird,
wherein the first and the second electrode down-leads are parallel
to each other, the third and fourth electrode down-leads are
parallel to each other, and the first and the second electrode
down-leads are insulated from the third and fourth electrode
down-leads respectively; and a thermionic electron emission unit,
the thermionic electron emission unit comprises a first electrode,
a second electrode, and a thermionic electron emitter, the first
electrode and the second electrode separately located and
electrically connected to the first electrode down-lead and the
third electrode down-lead respectively; wherein the thermionic
electron emitter comprises a carbon nanotube film structure.
2. The thermionic electron emission device as claimed in claim 1,
wherein the thermionic electron emitter is suspended above the
insulating substrate by the first electrode and the second
electrode.
3. The thermionic electron emission device as claimed in claim 1,
further comprising a plurality of recesses located on a surface of
the insulating substrate corresponding to a plurality of grids
respectively.
4. The thermionic electron emission device as claimed in claim 3,
wherein each of the plurality of recesses are the same size, and
each carbon nanotube film structure is located adjacent to one of
the plurality of recesses.
5. The thermionic electron emission device as claimed in claim 1,
wherein a plurality of grids form an array, the first electrodes in
a row of grids are electrically connected to the first electrode
down-lead, the second electrodes in a column of grids are
electrically connected to the third electrode down-lead.
6. The thermionic electron emission device as claimed in claim 1,
wherein a thickness of the first electrode and the second electrode
approximately ranges from 5 micrometers to 1 millimeter, and a
distance between the first electrode and the second electrode
approximately ranges from 50 micrometers to 1 millimeter.
7. The thermionic electron emission device as claimed in claim 1,
wherein the carbon nanotube film structure comprises at least one
layer of carbon nanotube film, and the carbon nanotube film
comprises a plurality of carbon nanotubes arranged along a
preferred orientation.
8. The thermionic electron emission device as claimed in claim 7,
wherein the carbon nanotube film structure comprises a carbon
nanotube film, and carbon nanotube film comprises a plurality of
carbon nanotubes joined end to end extending from the first
electrode to the second electrode.
9. The thermionic electron emission device as claimed in claim 7,
wherein the carbon nanotube film structure comprises at least two
stacked carbon nanotube films, the carbon nanotube films are
situated such that a preferred orientation of the carbon nanotubes
is set at an angle with respect to each other, the angle being
approximately ranges from 0.degree. to 90.degree..
10. The thermionic electron emission device as claimed in claim 7,
wherein a width of the carbon nanotube film approximately ranges
from 0.01 centimeters to 10 centimeters, and a thickness thereof
approximately ranges from 10 nanometers to 100 micrometers.
11. The thermionic electron emission device as claimed in claim 7,
wherein the carbon each nanotube film comprises a plurality of
successive and alike oriented carbon nanotube segments joined
end-to-end by van der Waals attractive force therebetween, each
carbon nanotube segment comprises a plurality of carbon nanotubes
parallel with each other, and the adjacent carbon nanotubes are
adhered by van der Waals attractive force therebetween.
12. A method for making a thermionic electron emission device, the
method comprising the following steps of: (a) providing an
insulating substrate; (b) forming a plurality of grids on the
insulating substrate; (c) fabricating a first electrode and a
second electrode in each grid on the insulating substrate; and (d)
placing a carbon nanotube film structure on the electrodes; and (e)
cutting away excess carbon nanotube film structure and keeping the
carbon nanotube film structure between the first electrode and the
second electrode in each grid.
13. The method as claimed in claim 12, wherein step (b) is executed
by a method selected from a group consisting of a screen-printing
method, a evaporation method, and a sputtering method.
14. The method as claimed in claim 13, wherein step (b) is executed
by screen printing: a plurality of uniformly-spaced first electrode
down-leads and second electrode down-leads parallel to each other
on the insulating substrate; a plurality of uniformly-spaced
insulating layers on the first electrode down-leads and second
electrode down-leads; and a plurality of third electrode down-lead,
fourth electrode down-leads on the insulating layers parallel to
each other on the insulating substrate.
15. The method as claimed in claim 14, wherein step (c) is executed
by fabricating a plurality of first electrodes on the first
electrode down-lead in each grid and a plurality of second
electrodes on the third electrode down-lead via a screen-printing
method, an evaporation method, or a sputtering method.
16. The method as claimed in claim 12, wherein step (d) further
comprises the following steps of: (d1) providing at least one
carbon nanotube film; and (d2) applying at least one carbon
nanotube film on the electrodes.
17. The method as claimed in claim 16, wherein step (d2) is
executed by applying one carbon nanotube film on the electrodes
along a direction extending from the first electrode to the second
electrode; or applying at least two stacked carbon nanotube films
on the insulating substrate and situated such that the carbon
nanotubes of one film are oriented at an angle with respect to the
carbon nanotubes of the adjacent film, the angle approximately
ranging from 0.degree. to 90.degree..
18. The method as claimed in claim 16, wherein step (d2) further
comprises the following steps: (d21) supplying a supporting
element; (d22) applying at least two carbon nanotube films side by
side on the supporting element along a direction extending from the
first electrode to the second electrode to form a carbon nanotube
film structure; (d23) cutting away any excess portion of the carbon
nanotube film structure; (d24) treating the carbon nanotube film
structure with an organic solvent; (d25) removing the carbon
nanotube film structure from the supporting element to form a
free-standing carbon nanotube film structure; and (d26) applying
the free-standing carbon nanotube film structure on the insulating
substrate.
19. The method as claimed in claim 18, further comprising applying
at least two stacked carbon nanotube films situated such that the
carbon nanotubes of one film are oriented at an angle with respect
to the carbon nanotubes of the adjacent film, the angle
approximately ranging from 0.degree. to 90.degree..
20. The method as claimed in claim 12, wherein the carbon nanotube
film structure applied on the electrodes is treated with an organic
solvent.
21. The method as claimed in claim 20, wherein the carbon nanotube
film structure can be treated by applying the organic solvent to
soak the entire surface of the carbon nanotube film structure or
immersing the carbon nanotube film structure in a container with
the organic solvent filled therein; the organic solvent is
volatilizable and can be selected from the group consisting of
ethanol, methanol, acetone, dichloroethane, chloroform, and
combinations thereof.
22. The method as claimed in claim 14, wherein step (e) is executed
by a laser ablation method or electron beam scanning method.
23. The method as claimed in claim 22, wherein step (e) is executed
by the laser ablation method includes the following steps of: (e1)
scanning the carbon nanotube film structure along each first
electrode down-lead via a laser beam; and (e2) scanning the carbon
nanotube film structure along each third electrode down-lead via a
laser beam to cut the carbon nanotube film structure applied on the
insulating substrate except that between the first electrodes and
the second electrodes, the laser beam having a power approximately
ranging from 10 watts to 50 watts and a speed approximately ranging
from 10 millimeters/second to 100 millimeters/second.
24. The method as claimed in claim 12, further comprises etching a
plurality of recesses on the insulating substrate.
Description
RELATED APPLICATIONS
[0001] This application is related to commonly-assigned
applications entitled, "METHOD FOR MAKING THERMIONIC ELECTRON
SOURCE", filed ______ (Atty. Docket No. US18567); "THERMIONIC
ELECTRON SOURCE", filed ______ (Atty. Docket No. US18568);
"THERMIONIC EMISSION DEVICE", filed ______ (Atty. Docket No.
US18570); "THERMIONIC EMISSION DEVICE", filed ______ (Atty. Docket
No. US18571); and "THERMIONIC ELECTRON SOURCE", filed ______ (Atty.
Docket No. US17306).
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to a thermionic electron
emission device adopting carbon nanotubes and a method for making
the same.
[0004] 2. Discussion of Related Art
[0005] Carbon nanotubes (CNT) are a carbonaceous material and have
received much interest since the early 1990s. Carbon nanotubes have
interesting and potentially useful electrical and mechanical
properties. Due to these and other properties, CNTs have become a
significant contributor to the research and development of electron
emitting devices, sensors, and transistors, among other
devices.
[0006] Generally, there are two kinds of electron-emitting devices;
field emission device and thermionic electron emission device. The
field emission device includes an insulating substrate, and a
plurality of grids located thereon. Each grid includes first,
second, third and fourth electrode down-leads located on the
periphery of the gird. The first and the second electrode
down-leads are parallel to each other. The third and fourth
electrode down-leads are parallel to each other. The first and the
second electrode down-leads are insulated from the third and fourth
electrode down-leads.
[0007] The thermionic electron emission device, conventionally,
comprises a plurality of thermionic electron emission units. Each
thermionic electron emission unit includes a thermionic electron
emitter and two electrodes. The thermionic electron emitter is
located between the two electrodes and electrically connected
thereto. The thermionic emitter is generally made of a metal, a
boride or an alkaline earth metal carbonate. The thermionic
emitter, made of metal, can be a metal ribbon or a metal thread,
and is fixed between the two electrodes by welding. The boride or
alkaline earth metal carbonate can be dispersed in conductive
slurry, wherein the conductive slurry is directly coated or sprayed
on a heater. The heater can be secured between the two electrodes
as a thermionic electron emitter. However, it is hard to assemble a
plurality of thermionic electron emission units, and the assembled
thermionic electron emission device cannot realize uniform
thermionic emission. Further, the size of the thermionic emitter
using the metal, boride or alkaline earth metal carbonate is large,
and thereby limits its application in micro-devices. Furthermore,
the coating formed by direct coating or from spraying the metal,
boride or alkaline earth metal carbonate has a high resistivity,
and thus, the thermionic electron source using the same has greater
power consumption and is therefore not suitable for applications
involving high current density and brightness.
[0008] What is needed, therefore, is a thermionic electron emission
device and a method for making the same, wherein the thermionic
electron emission device has excellent thermal electron emitting
properties, and can be used in flat panel displays with high
current density and brightness, logic circuits, as well as in other
fields using thermionic electron emission devices.
SUMMARY
[0009] In one embodiment, a thermionic electron emission device
includes an insulating substrate, and one or more grids located
thereon. The one or more grids include(s) a first, second, third
and fourth electrode down-leads located on the periphery thereof,
and a thermionic electron emission unit therein. The first and
second electrode down-leads are parallel to each other. The third
and fourth electrode down-leads are parallel to each other. The
first and second electrode down-leads are insulated from the third
and fourth electrode down-leads. The thermionic electron emission
unit includes a first electrode, a second electrode, and a
thermionic electron emitter. The first electrode and the second
electrode are separately located and electrically connected to the
first electrode down-lead and the third electrode down-lead
respectively. Wherein the thermionic electron emitter includes a
carbon nanotube film structure.
[0010] Other novel features and advantages of the present
thermionic electron emission device and method for making the same
will become more apparent from the following detailed description
of exemplary embodiments when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Many aspects of the present thermionic electron emission
device and method for making the same can be better understood with
references to the following drawings. The components in the
drawings are not necessarily drawn to scale, the emphasis instead
being placed upon clearly illustrating the principles of the
present thermionic electron emission device and method for making
the same.
[0012] FIG. 1 is an exploded, isometric view of a thermionic
electron emission device in accordance with the present
embodiment.
[0013] FIG. 2 shows a Scanning Electron Microscope (SEM) image of a
carbon nanotube film used in the thermionic electron emission
device of FIG. 1.
[0014] FIG. 3 is a structural schematic of a carbon nanotube
segment.
[0015] FIG. 4 is a flow chart of a method for making a thermionic
electron emission device, in accordance with the present
embodiment.
[0016] Corresponding reference characters indicate corresponding
parts throughout the views. The exemplifications set out herein
illustrate at least one preferred embodiment of the present
thermionic electron emission device and method for making the same,
in at least one form, and such exemplifications are not to be
construed as limiting the scope of the invention in any manner.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0017] References will now be made to the drawings to describe, in
detail, embodiments of the present thermionic electron emission
device and method for making the same.
[0018] Referring to FIG. 1, a thermionic electron emission device
200 includes an insulating substrate 202, and one or more grids 214
located thereon. Each grid 214 includes a first electrode down-lead
204a, a second electrode down-lead 204b, a third electrode
down-lead 206a, a fourth electrode down-lead 206b located on the
periphery of the gird 214, and a thermionic electron emission unit
220 located in each grid 214. The first electrode down-lead 204a
and the second electrode down-lead 204b are parallel to each other.
The third electrode down-lead 206a and the fourth electrode
down-leads 206b are parallel to each other. Furthermore, a
plurality of insulating layers 216 is sandwiched between the first
and second electrode down-leads 204a, 204b, and the third and
fourth electrode down-leads 206a, 206b to avoid short-circuiting.
It is to be understood that the electrode down-leads of one grid
can be a different electrode down-leads to an adjacent gird. For
example, the same electrode down-leads can be the first for one
grid and a second for an adjacent one.
[0019] One thermionic electron emission unit 220 is located in each
grid 214. Each thermionic electron emission unit 220 includes a
first electrode 210, a second electrode 212, and a thermionic
electron emitter 208. The first electrode 210 and the second
electrode 212 are separately located in the grid 214, and
electrically connected to the thermionic electron emitter 208. The
thermionic electron emitter 208 is suspended above the insulating
substrate 202 by the first electrode 210 and the second electrode
212. The thermionic electron emitter 208 can be a carbon nanotube
film structure. The first electrode 210 is electrically connected
to a first electrode down-lead 204a. The second electrode 212 is
electrically connected to a third electrode down-lead 206a. A
plurality of grids 214 form an array, the first electrodes 210 in a
row of grids 214 are electrically connected to a first electrode
down-lead 204a, the second electrodes 212 in a column of grids 214
are electrically connected to a third electrode down-lead 206a. In
the present embodiment, rows are perpendicular to columns.
[0020] The insulating substrate 202 is insulative, and can be made
of ceramics, glass, resins, or quartz, among other materials. A
size and shape of the insulating substrate 202 can be set as
desired. In the present embodiment, the insulating substrate 202 is
a glass substrate. Thickness of the insulating substrate 202 is
greater than 1 millimeter, and length/width of the insulating
substrate is greater than 1 centimeter. The insulating substrate
202 can further include a plurality of recesses 218 located on the
insulating substrate 202 corresponding to the grids 214. The
recesses 218 are all the same size and uniformly-spaced. Part of
the thermionic electron emitter 208 is suspended above the surface
of the insulating substrate 202 corresponding to the recesses 218.
Therefore there is a spacing between the thermionic electron
emitter 208 and the insulating substrate 202. Since the spacing has
better thermal insulative properties than the direct contact with
the substrate, the thermionic electron emitter 208 will transfer
less energy applied for heating the insulating substrate 202, and
as a result, the thermionic electron emission device 200 will have
an excellent thermionic emitting property.
[0021] The first through fourth electrode down-leads 204a, 204b,
206a, 206b can be conductors, e.g., metal layers. In the present
embodiment, the first through fourth electrode down-leads 204a,
204b, 206a, 206b are strip-shaped planar conductors formed by a
screen-printing method. Widths of the first through fourth
down-leads 204a, 204b, 206a, 206b approximately range from 30
micrometers to 1 millimeter, and thicknesses thereof approximately
range from 5 micrometers to 1 millimeter, and distances
therebetween approximately range from 300 micrometers to 5
millimeters. The first electrode down-lead 204a and the second
electrode down-lead 204b cross the third electrode down-lead 206a
and the fourth electrode down-leads 206b respectively. A preferred
orientation of the first through fourth electrode down-leads 204a,
204b, 206a, 206b is with them set at an angle with respect to each
other. The angle approximately ranges from 10.degree. to
90.degree.. In the present embodiment, the angle is 90.degree.. In
the present embodiment, the first through fourth electrode
down-leads 204a, 204b, 206a, 206b can be formed by printing
conductive slurry on the insulating substrate 202 via a
screen-printing method. The conductive slurry includes metal
powder, low-melting glass powder and adhesive. The metal powder can
be silver powder, and the adhesive can be ethyl cellulose or
terpineol. A weight ratio of the metal powder in the conductive
slurry approximately ranges from 50% to 90%. A weight ratio of the
low-melting glass powder in the conductive slurry approximately
ranges from 2% to 10%. A weight ratio of the adhesive in the
conductive slurry approximately ranges from 10% to 40%.
[0022] The first electrode 210 and the second electrode 212 can be
conductors, e.g., metal layers. In the present embodiment, the
first electrode 210 and the second electrode 212 are planar
conductors formed by a screen-printing method. Sizes of the first
electrode 210 and the second electrode 212 are determined by the
size of the grid 214. Lengths of the first electrode 210 and the
second electrode 212 approximately range from 30 micrometers to 1
millimeter, widths thereof approximately range from 30 micrometers
to 1 millimeter, and thicknesses thereof approximately range from 5
micrometers to 1 millimeter. A distance between the first electrode
210 and the second electrode 212 approximately ranges from 50
micrometers to 1 millimeter. In the present embodiment, a length of
the first electrode 210 and the second electrode 212 is 60
micrometers, a width of each is 40 micrometers, and a thickness of
each is 20 micrometers. The first electrode 210 and the second
electrode 212 can be formed by printing conductive slurry on the
insulating substrate 202 via screen-printing. Ingredients of the
conductive slurry are the same as the conductive slurry used to
form the electrode down-leads.
[0023] The carbon nanotube film structure includes at least one
carbon nanotube film. Referring to FIGS. 2 and 3, each carbon
nanotube film comprises a plurality of successively oriented carbon
nanotube segments 143 joined end-to-end by van der Waals attractive
force. Each carbon nanotube segment 143 includes a plurality of
carbon nanotubes 145 parallel to each other, and combined by van
der Waals attractive force. The carbon nanotubes 145 in the carbon
nanotube film are also oriented along a preferred orientation. The
thermionic electron emitter 208 includes a carbon nanotube film,
and the carbon nanotubes 145 therein extend from the first
electrode 210 to the second electrode 212. In other embodiments,
the carbon nanotube film structure includes at least two carbon
nanotube films combined by van der Waals attractive force. The
films are situated such that an orientation of the carbon nanotubes
in one film is at an angle with respect to orientation of the
carbon nanotubes in the other film. The angle approximately ranges
from 0.degree. to 90.degree..
[0024] In the present embodiment, the carbon nanotube film is
acquired by pulling from a carbon nanotube array grown on a 4-inch
base. A width of the acquired carbon nanotube film approximately
ranges from 0.01 to 10 centimeters. A thickness of the acquired
carbon nanotube film approximately ranges from 10 nanometers to 100
micrometers. Furthermore, the carbon nanotube film can be cut into
smaller predetermined sizes and shapes. The carbon nanotubes in the
carbon nanotube film are selected from a group consisting of
single-walled carbon nanotubes, double-walled carbon nanotubes, and
multi-walled carbon nanotubes. Diameters of the single-walled
carbon nanotubes approximately range from 0.5 to 10 nanometers.
Diameters of the double-walled carbon nanotubes approximately range
from 1 to 50 nanometers. Diameters of the multi-walled carbon
nanotubes approximately range from 1.5 to 50 nanometers. Since the
carbon nanotube film has a high surface-area-to-volume ratio, the
carbon nanotube film may easily adhere to other objects. Thus, the
carbon nanotube film can directly be fixed on the insulating
substrate 202 or other carbon nanotube films because of the
adhesive properties of the carbon nanotubes. The thermionic
electron emitter 208 made by the carbon nanotubes can also be fixed
on the insulating substrate 202 via adhesive or conductive
glue.
[0025] Referring to FIG. 4, a method for making a thermionic
electron emission device includes the following steps of: (a)
providing an insulating substrate; (b) forming a plurality of grids
on the insulating substrate; (c) fabricating a first electrode and
a second electrode in each grid on the insulating substrate; (d)
placing a carbon nanotube film structure on the electrodes; and (e)
cutting away excess carbon nanotube film structure and keeping the
carbon nanotube film structure between the first electrode and the
second electrode in each grid.
[0026] In step (a), the insulating substrate can be made of
ceramics, glass, resins, or quartz, among other insulating
materials. In the present embodiment, the insulating substrate is a
glass substrate. Step (a) can further includes a step of etching a
plurality of uniformly-spaced recesses with a predetermined size on
the insulating substrate.
[0027] Step (b) can be executed by screen printing a plurality of
uniformly-spaced first electrode down-leads and second electrode
down-leads parallel to each other on the insulating substrate; a
plurality of uniformly-spaced insulating layers on the first
electrode down-leads and second electrode down-leads; and a
plurality of third electrode down-lead, fourth electrode down-leads
on the insulating layers parallel to each other on the insulating
substrate. The first and second electrode down-leads are insulated
from the third and fourth electrode down-leads by the insulating
layer at the crossover regions thereof. The first through fourth
electrode down-leads can be electrically connected together by a
connection external to the grid. It can be understood that the
plurality of recesses can also be formed after step (b).
[0028] Step (c) can be executed by fabricating a plurality of first
electrodes on the first electrode down-lead and a plurality of
second electrodes on the third electrode down-lead corresponding to
each grid via a screen-printing method, an evaporation method, or a
sputtering method.
[0029] In step (c), in the present embodiment, a screen-printing
method can be used to make the first electrodes and the second
electrodes. The first electrode and the second electrode are
located a certain distance apart. The first electrode is
electrically connected to the first electrode down-lead, and the
second electrode is electrically connected to the second electrode
down-lead.
[0030] Step (d) includes the following steps of: (d1) providing at
least one carbon nanotube film; and (d2) applying the at least one
carbon nanotube film on the electrodes.
[0031] Step (d1) includes the following steps of: (d11) providing
an array of carbon nanotubes or super-aligned array of carbon
nanotubes; and (d12) pulling out a carbon nanotube film from the
array of carbon nanotubes, by using a tool.
[0032] In step (d11), a given super-aligned array of carbon
nanotubes can be formed by the following substeps: firstly,
providing a substantially flat and smooth substrate; secondly,
forming a catalyst layer on the substrate; thirdly, annealing the
substrate with the catalyst layer thereon in air at a temperature
approximately ranging from 700.degree. C. to 900.degree. C. for
about 30 to 90 minutes; fourthly, heating the substrate with the
catalyst layer to a temperature approximately ranging from
500.degree. C. to 740.degree. C. in a furnace with a protective gas
therein; and fifthly, supplying a carbon source gas to the furnace
for about 5 to 30 minutes and growing the super-aligned array of
carbon nanotubes on the substrate.
[0033] The substrate can be a P-type silicon wafer, an N-type
silicon wafer, or a silicon wafer with a film of silicon dioxide
thereon. In the present embodiment, a 4-inch P-type silicon wafer
is used as the substrate. The catalyst can be made of iron (Fe),
cobalt (Co), nickel (Ni), or any alloy thereof. The protective gas
can be made up of at least one of nitrogen (N.sub.2), ammonia
(NH.sub.3), and a noble gas. In step (a5), the carbon source gas
can be a hydrocarbon gas, such as ethylene (C.sub.2H.sub.4),
methane (CH.sub.4), acetylene (C.sub.2H.sub.2), ethane
(C.sub.2H.sub.6), or any combination thereof.
[0034] The super-aligned array of carbon nanotubes can be
approximately 200 to 400 microns in height and include a plurality
of carbon nanotubes parallel to each other and approximately
perpendicular to the substrate. The carbon nanotubes in the array
can be selected from a group consisting of single-walled carbon
nanotubes, double-walled carbon nanotubes, or multi-wall carbon
nanotubes. A diameter of the single-walled carbon nanotubes
approximately ranges from 0.5 to 50 nanometers. A diameter of the
double-walled carbon nanotubes approximately ranges from 1 to 10
nanometers. A diameter of the multi-walled carbon nanotubes
approximately ranges from 1.5 to 10 nanometers.
[0035] The super-aligned array of carbon nanotubes formed under the
above conditions is essentially free of impurities such as
carbonaceous or residual catalyst particles. The carbon nanotubes
in the super-aligned array are closely packed together by the van
der Waals attractive force.
[0036] Step (d12) can be executed by selecting a one or more carbon
nanotubes having a predetermined width from the array of carbon
nanotubes; and pulling the carbon nanotubes to form nanotube
segments at an even/uniform speed to achieve a uniform carbon
nanotube film.
[0037] The carbon nanotube segments can be selected by using an
adhesive tape such as the tool to contact with the super-aligned
array. The pulling direction is substantially perpendicular to the
growing direction of the super-aligned array of carbon
nanotubes.
[0038] More specifically, during the pulling process, as the
initial carbon nanotube segments are drawn out, other carbon
nanotube segments are also drawn out end-to-end due to the van der
Waals attractive force between ends of adjacent segments. This
process of drawing ensures a substantially continuous and uniform
carbon nanotube film can be formed. The carbon nanotubes in the
carbon nanotube film are all substantially parallel to the
pulling/drawing direction of the carbon nanotube film, and the
carbon nanotube film produced in such manner can be selectively
formed having a predetermined width. The carbon nanotube film
formed by the pulling/drawing method has superior uniformity of
thickness and conductivity over a disordered carbon nanotube film.
Furthermore, the pulling/drawing method is simple, fast, and
suitable for industrial applications. It is to be understood that
some variation can occur in the orientation of the nanotubes in the
film as can be seen in FIG. 2.
[0039] Step (d2) can be executed by applying one carbon nanotube
film on the electrodes along a direction extending from the first
electrode to the second electrode. Step (d2) also can be executed
by applying at least two stacked carbon nanotube films on the
electrodes situated such that the carbon nanotubes of one film are
oriented at an angle with respect to the carbon nanotubes of the
adjacent film, the angle approximately ranging from 0.degree. to
90.degree..
[0040] Step (d2) also can be executed by the following steps: (d21)
supplying a supporting element; (d22) applying at least two carbon
nanotube films side by side on the supporting element along a
direction extending from the first electrode to the second
electrode to form a carbon nanotube film structure; (d23) cutting
away any excess portion of the carbon nanotube film structure;
(d24) treating the carbon nanotube film structure with an organic
solvent; (d25) removing the carbon nanotube film structure from the
supporting element to form a free-standing carbon nanotube film
structure; and (d26) applying the free-standing carbon nanotube
film structure on the insulating substrate. Step (d2) further
includes a step of applying with at least two stacked carbon
nanotube films such that orientation of the carbon nanotubes in one
film are set at an angle with respect to the carbon nanotubes in
the adjacent films to form a carbon nanotube film structure, the
angle approximately ranging from 0.degree. to 90.degree.. Since the
carbon nanotube film has a high surface-area-to-volume ratio, the
carbon nanotube film structure formed by at least one carbon
nanotube film may easily adhere to other objects. Thus, the carbon
nanotube film can directly be fixed on the insulating substrate due
to the adhesive properties of the nanotubes. The carbon nanotube
structure can also be secured on the insulating substrate via
adhesive or conductive glue.
[0041] The carbon nanotube film structure secured on the electrodes
can be treated with an organic solvent. The carbon nanotube film
structure can be treated by applying organic solvent to soak the
entire surface of the carbon nanotube film structure or immersing
the carbon nanotube film structure in a container with organic
solvent filled therein. The organic solvent is volatilizable and
can be selected from the group consisting of ethanol, methanol,
acetone, dichloroethane, chloroform, and combinations thereof. In
the present embodiment, the organic solvent is ethanol. After being
soaked by the organic solvent, microscopically, carbon nanotube
strings will be formed by some of the adjacent carbon nanotubes
bundling in the carbon nanotube film due to the surface tension of
the organic solvent. In one aspect, part of the carbon nanotubes in
the untreated carbon nanotube film that are not adhered on the
substrate will adhere on the substrate after the organic solvent
treatment due to the surface tension of the organic solvent. Then
the contacting area of the carbon nanotube film with the substrate
will increase, and thus, the treated carbon nanotube film can more
firmly adhere to the surface of the substrate. In another aspect,
due to the decrease of the specific surface area via bundling, the
mechanical strength and toughness of the carbon nanotube film are
increased and the coefficient of friction of the carbon nanotube
films is reduced. Macroscopically, the film will be an
approximately uniform carbon nanotube film.
[0042] Further, at least one fixing electrode (not shown), formed
on the carbon nanotube film structure corresponding to the first
electrode and the second electrode, can be further provided to fix
the carbon nanotube film structure on the first electrode and the
second electrode firmly.
[0043] Step (e) can be executed by a laser ablation method or an
electron beam scanning method. In the present embodiment, step (e)
is executed by a laser ablation method. Step (e) includes the
following steps of: (e1) scanning the carbon nanotube film
structure along each first electrode down-lead via a laser beam,
and (e2) scanning the carbon nanotube film structure along each
third electrode down-lead via a laser beam to cut the carbon
nanotube film structure applied on the insulating substrate except
that between the first electrodes and the second electrodes. The
laser beam has a power approximately ranging from 10 watts to 50
watts and a scanning speed approximately ranging from 10
millimeters/second to 5000 millimeters/second. In the present
embodiment, the power of the laser beam is 30 watts; a scanning
speed thereof is 100 millimeters/second.
[0044] In step (e1), a width of the laser beam is equal to a
distance between the adjacent first electrodes along the aligned
direction of the third electrode down-lead, and approximately
ranges from 20 micrometers to 500 micrometers. Step (e1) is
executed to cut the carbon nanotube film structure between adjacent
second electrodes in adjacent grid respectively along the aligned
direction of the third electrode down-lead. In step (e2), a width
of the laser beam is equal to a distance between adjacent first
electrode and second electrode in adjacent grid respectively along
the aligned direction of the first electrode down-lead, and
approximately ranges from 20 micrometers to 500 micrometers. Step
(e2) is executed to cut the carbon nanotube film structure between
adjacent first electrode and second electrode in adjacent grid
respectively along the aligned direction of the first electrode
down-lead.
[0045] Compared to conventional technologies, the method for making
the thermionic electron emission device provided by the present
embodiments has many advantages including the following. Firstly,
since the carbon nanotube film structure is formed by at least one
carbon nanotube film pulled from a carbon nanotube array, the
method is simple and low-cost. Secondly, since the carbon nanotubes
in the carbon nanotube film structure are uniformly distributed,
the thermionic electron emitter adopting the carbon nanotube film
structure prepared by the present embodiment can acquire a uniform
and stable thermal electron emissions state. Thirdly, since the
thermionic electron emitter and the insulating substrate are
separately located (a space located therebetween), the insulating
substrate will transfer less energy for heating the thermionic
electron emitter to the atmosphere in the process of heating, and
as a result, the thermionic electron emission device will have an
excellent thermionic emitting property. Finally, since the carbon
nanotube film structure has a small width and a low resistance, the
thermionic electron emission device adopting the carbon nanotube
film structure can emit electrons at a low thermal power, thus the
thermionic electron emission device can be used for high current
density and high brightness of the flat panel display and logic
circuits, among other fields.
[0046] Finally, it is to be understood that the above-described
embodiments are intended to illustrate rather than limit the
invention. Variations may be made to the embodiments without
departing from the spirit of the invention as claimed. The
above-described embodiments illustrate the scope of the invention
but do not restrict the scope of the invention.
[0047] It is also to be understood that the above description and
the claims drawn to a method may include some indication in
reference to certain steps. However, the indication used is only to
be viewed for identification purposes and not as a suggestion as to
an order for the steps.
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